There is a great need for fault-tolerant apparatus for controlling fan blade pitch of turbofan engines. In the event of a single failure, non-fault tolerant apparatus would not be able to control the position of the fan blades.
Apparatus for controlling blade pitch can be made fault-tolerant by providing redundant controllers. One controller is designated as a primary controller and the remaining controllers provide backups in succession. Two controllers provide tolerance to a single failure, three controllers provide tolerance to two failures and so on.
There are drawbacks to such fault-tolerant apparatus. To provide tolerance to a single fault, the number of components must be doubled. Also doubled is the weight and cost of the system. As the redundancy is further increased, the weight and cost of the system is increased proportionately.